Production of xylenes from syngas

ABSTRACT

This disclosure relates to the production of xylenes from syngas, in which the syngas is converted to an aromatic product by reaction with a Fischer-Tropsch catalyst and an aromatization catalyst. The Fischer-Tropsch catalyst and aromatization catalyst may be different catalysts or combined into a single catalyst. The aromatic product is then subjected to selective alkylation with methanol and/or carbon monoxide and hydrogen to increase its p-xylene content.

PRIORITY CLAIM

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 62/028,490, filed Jul. 24, 2014, which is incorporatedby reference in its entirety.

FIELD

This disclosure relates to the production of xylenes from syngas.

BACKGROUND

The isomers of xylene find wide and varied application. For example,meta-xylene (m-xylene) is used in the manufacture of dyes, andortho-xylene (o-xylene) is used as a feedstock for producing phthalicanhydride, which finds use in the manufacture of plasticizers. However,currently the most valuable of the xylene isomers is para-xylene(p-xylene), since p-xylene is a feedstock for terephthalic acid, whichin turn is used in the manufacture of polyester fibers and films.

The majority of p-xylene produced today is derived from crude oil viareforming of the naphtha portion of the crude into a mixture of benzene,toluene, and xylenes (BTX) and heavier aromatics. These aromatics thenundergo a variety of reactions, such as transalkylation,disproportionation and xylene isomerization, to increase theconcentration of p-xylene. The current commercial process also requiresextraction of aromatics from non-aromatics and separation of p-xylenefrom a mixture of xylene isomers via crystallization or molecular sieveadsorption. The overall process is therefore complex. Moreover, as crudeoil prices rise, so does the feed stock price for p-xylene productionvia the current commercial routes. Recently, as crude prices have risen,the prices of coal and natural gas having fallen making syngas derivedfrom these sources cheaper on a carbon or energy equivalent basis and apotentially attractive feed for the production of basic chemicals, suchas p-xylene.

The conversion of syngas to olefins and paraffins has been widelypracticed for many years via the Fischer-Tropsch process and indirectlyvia the methanol to olefins (MTO) process. However, both of these syngasconversion routes produce only small amounts of aromatics and there istherefore a need for an improved route for converting syngas toaromatics and particularly p-xylene.

In a paper entitled “Direct Conversion of Syngas into Aromatics overBifunctional Fe/MnO—ZnZSM-5 Catalyst”, Chinese Journal of Catalysis,Volume 23, No. 4 July, 2002, Wang Desheng et al. report that syngas canbe converted into aromatics at high yield using a bifunctional catalystcomprising Fe/MnO mixed with Zn-ZSM-5 containing up to 7 wt % Zn underconditions including a temperature of 517° F. (270° C.), a pressure of1100 kpa (absolute), and a hydrogen to carbon monoxide molar ratio of2:1. However, the aromatic product slate obtained in the process of Wanget al. is composed mainly of benzene and toluene, rather than the moredesirable p-xylene. There is, therefore, an ongoing need to provide aprocess of converting syngas to aromatics in which the yield of xyleneisomers, and in particular p-xylene, is improved.

SUMMARY

The present invention is directed to efficiently and cost effectivelyproducing p-xylene by combining a para-selective toluene/benzenemethylation reaction with an initial aromatics-selective syngasconversion process employing a Fischer-Tropsch catalyst and anaromatization catalyst. The process comprises contacting a first feedcomprising hydrogen and carbon monoxide in a molar ratio of hydrogen tocarbon monoxide from about 0.5 to 6 with (i) a first catalyst comprisingat least one metal or compound containing a metal selected from thegroup consisting of Fe, Co, Cr, Cu, Zn, Mn, and Ru, and (ii) a secondcatalyst, which may be the same as or different than the first catalyst,comprising at least one molecular sieve under conditions including atemperature from about 200° C. to 370° C. and a pressure from about 500to 3000 kPa (absolute) effective to produce a reaction effluentcontaining benzene and/or toluene. At least part of the benzene and/ortoluene in the reaction effluent is then reacted with a second feedcomprising methanol and/or hydrogen and carbon monoxide under conditionseffective to alkylate the benzene and toluene and produce xylenes. Thealkylation reaction may be conducted in the presence of a third catalystcomprising at least one molecular sieve having a Diffusion Parameter for2,2-dimethylbutane of from 0.1 to 15 sec⁻¹ when measured at atemperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8kPa).

The invention further provides a catalyst system comprising a firstcatalyst comprising at least one metal or compound containing a metalselected from the group consisting of Fe, Co, Cr, Cu, Zn, Mn, and Ru,and a second catalyst, which may be the same as or different than thefirst catalyst, comprising at least one molecular sieve and at least onemetal from Groups 10-14 of the Periodic Table or compound thereof, withthe first and second catalysts located within the same reactor bed.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a graph showing the calculated equilibrium concentrationsfor exemplary components of the effluent from the conversion of syngaswith varying H₂/CO molar compositions at a temperature of 270° C. and apressure of 1100 kPa (absolute). The xylene isomers were restricted top-xylene in the calculation to show the maximum potential yield from ashape selective catalyst. In the FIGURE, the line through the squarepoints designates H₂, the line through the triangular points designatesCO, the line through the diamond points designates CO₂, the line throughthe circular points designates H₂O, the line through the asterisk pointsdesignates p-xylene, the line through the cross points designatestoluene, and the line through the “plus” symbol point designatesbenzene.

DETAILED DESCRIPTION

The present disclosure relates to a process for the production ofxylenes, and particularly p-xylene, from syngas. In certain aspects, thesyngas is initially converted to a hydrocarbon product containingbenzene and/or toluene using a multi-functional catalyst systemcomprising a Fischer-Tropsch catalyst and an aromatization catalyst,which may be different catalysts or combined into a single catalyst. Atleast part of the benzene and/or toluene is then alkylated with methanoland/or hydrogen and carbon monoxide over an alkylation catalystselective for the production of p-xylene.

Definitions

For the purpose of this specification and appended claims, the followingterms are defined. The term “C_(n)” hydrocarbon wherein n is a positiveinteger, e.g., 1, 2, 3, 4, or 5, means a hydrocarbon having n number ofcarbon atom(s) per molecule. The term “C_(n+)” hydrocarbon wherein n isa positive integer, e.g., 1, 2, 3, 4, or 5, means hydrocarbon having atleast n number of carbon atom(s) per molecule. The term “C_(n−)”hydrocarbon wherein n is a positive integer, e.g., 1, 2, 3, 4, or 5,means hydrocarbon having no more than n number of carbon atom(s) permolecule. The term “aromatics” means hydrocarbon molecules containing atleast one aromatic core. The term “hydrocarbon” encompasses mixtures ofhydrocarbon, including those having different values of n. The term“syngas” means a gaseous mixture comprising hydrogen, carbon monoxide,and optionally some carbon dioxide.

As used herein, the numbering scheme for the groups of the PeriodicTable of the Elements is as disclosed in Chemical and Engineering News,63(5), 27 (1985).

Syngas-Containing Feed

The syngas-containing feed employed in the present process compriseshydrogen and at least 4 mol. %, for example at least 10 mol. %, ofcarbon monoxide, such that the molar ratio of hydrogen to carbonmonoxide in the feed is from about 0.5 to 20, preferably from about 0.5to 6, more preferably from about 0.6 to 10 or from about 0.8 to 4, andmost preferably from about 1 to 3. In a preferred embodiment, the molarratio of hydrogen to carbon monoxide is from about 0.5 to 6.

The syngas can be produced from methane and/or other carbon-containingsource material. The type of carbon-containing source material used isnot critical. The source material can comprise, e.g., methane and otherlower (C₄—) alkanes, such as contained in a natural gas stream, orheavier hydrocarbonaceous materials, such as coal and biomass.Desirably, the source material comprises ≧10 vol. %, such as ≧50 vol. %,based on the volume of the source material, of at least one hydrocarbon,especially methane.

The source material can be converted to syngas by any convenient method,including those well-established in the art. Suitable methods includethose described in U.S. Patent Application Publication Nos. 2007/0259972A1, 2008/0033218 A1, and 2005/0107481 A1, each of which is incorporatedby reference herein in its entirety.

For example, natural gas can be converted to syngas by steam reforming.This normally involves the initial removal of inert components in thenatural gas, such as nitrogen, argon, and carbon dioxide. Natural gasliquids can also be recovered and directed to other processing ortransport. The purified natural gas is then contacted with steam in thepresence of a catalyst, such as one or more metals or compounds thereofselected from Groups 7 to 10 of the Periodic Table of the Elementssupported on an attrition resistant refractory support, such as alumina.The contacting is normally conducted at high temperature, such as in therange of from 800° C. to 1100° C., and pressures ≦5000 kPa. Under theseconditions, methane converts to carbon monoxide and hydrogen accordingto reactions such as:CH₄+H₂O═CO+3H₂.

Steam reforming is energy intensive in that the process consumes over200 kJ/mole of methane consumed. A second method of producing syngasfrom methane is partial oxidation, in which the methane is burned in anoxygen-lean environment. The methane is partially-oxidized to carbonmonoxide (reaction (i)), with a portion of the carbon monoxide beingexposed to steam reforming conditions (reaction (ii)) to producemolecular hydrogen and carbon dioxide, according to the followingrepresentative reactions:CH₄+ 3/2O₂═CO+2H₂O  (i),CO+H₂O═CO₂+H₂  (ii).

Partial oxidation is exothermic and yields a significant amount of heat.Because steam reforming reaction is endothermic and partial oxidation isexothermic, these two processes are often performed together forefficient energy usage. Combining the steam reforming and partialoxidation yields a third process for generating syngas from natural gasin which the heat generated by partial oxidation is used to drive steamreforming to yield syngas.

Production of Xylenes from Syngas Via Fischer-TropschSynthesis/Aromatization Followed by Selective Alkylation

In certain aspects, the present disclosure provides a process forproducing xylenes in which syngas is initially converted to a productcomprising aromatics, with benzene and toluene being the primaryproducts, and at least part of the resultant benzene and toluene ismethylated over a para-selective alkylation catalyst to producep-xylene. The p-xylene can then be recovered by conventional techniques,such as adsorption and/or crystallization.

The initial syngas conversion to an aromatic-containing product involvesa multi-step process in which the syngas is reacted over a firstcatalyst, a Fischer-Tropsch (F-T) catalyst comprising at least one metalor compound thereof selected from Fe, Co, Cr, Cu, Zn, Mn and Ru underconditions effective to convert hydrogen and carbon monoxide into afirst product mixture containing C₂+ olefins and paraffins. The firstproduct mixture is then reacted in the presence of a second catalyst, anaromatization catalyst comprising at least one molecular sieve underconditions effective to produce benzene and toluene.

The first catalyst, which has F-T functionality, may comprise a singleactive metallic species or may comprise a multimetallic, such as abimetallic or trimetallic, composition. In most cases the metals aresupported onto zinc oxide, manganese oxide, alumina, silica, carbon, andmixtures thereof and optionally at least one stabilizer selected from anelement or compound thereof from Groups 1 to 4, such as Cs, K, and/orCa, for improving the metal dispersion. For example the first catalystmay comprise a combination of Fe and Cu or Co either in metallic oroxide form or a combination thereof. The amount of active metallicspecies present in the first catalyst can vary widely depending on theparticular metal or metals present in the catalyst. For example, wherethe first catalyst comprises a combination of Fe and Cu, the catalystcan contain from 1 to 50 wt % of Fe and from 0.1 to 20 wt % of Cu, bothon total catalyst weight basis. The active metallic species of the firstcatalyst may also be unsupported and in this case would comprise 20-99%Fe and from 1-80% Cu.

Reaction of the syngas in the presence of the first catalyst to producethe first product mixture via F-T synthesis may be conducted over a widerange of temperature and pressures, although generally temperatures lessthan 400° C. are desirable. Thus in certain embodiments, the reaction isconducted at a temperature from 200° C. to 370° C. and a pressure from500 to 3000 kPa (absolute), for example at a temperature from 250° C. to350° C. and a pressure from 700 to 2000 kPa (absolute). Under theseconditions, at least 50% conversion of the CO in the feed may beachieved.

The second catalyst, which has an aromatization functionality, comprisesat least one molecular sieve and, in certain aspects, at least onemedium pore size molecular sieve having a Constraint Index of 2-12 (asdefined in U.S. Pat. No. 4,016,218). Examples of such medium poremolecular sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35,ZSM-48, and mixtures and intermediates thereof. ZSM-5 is described indetail in U.S. Pat. Nos. 3,702,886 and Re. 29,948. ZSM-11 is describedin detail in U.S. Pat. No. 3,709,979. A ZSM-5/ZSM-11 intermediatestructure is described in U.S. Pat. No. 4,229,424. ZSM-12 is describedin U.S. Pat. No. 3,832,449. ZSM-22 is described in U.S. Pat. No.4,556,477. ZSM-23 is described in U.S. Pat. No. 4,076,842. ZSM-35 isdescribed in U.S. Pat. No. 4,016,245. ZSM-48 is more particularlydescribed in U.S. Pat. No. 4,234,231.

In other aspects, the second catalyst employed in the present processcomprises at least one molecular sieve of the MCM-22 family. As usedherein, the term “molecular sieve of the MCM-22 family” (or “material ofthe MCM-22 family” or “MCM-22 family material” or “MCM-22 familyzeolite”) includes one or more of:

(i) molecular sieves made from a common first degree crystallinebuilding block unit cell, which unit cell has the MWW frameworktopology. (A unit cell is a spatial arrangement of atoms which if tiledin three-dimensional space describes the crystal structure. Such crystalstructures are discussed in the “Atlas of Zeolite Framework Types”,Fifth edition, 2001, the entire content of which is incorporated asreference);

(ii) molecular sieves made from a common second degree building block,being a 2-dimensional tiling of such MWW framework topology unit cells,forming a monolayer of one unit cell thickness, preferably one c-unitcell thickness;

(iii) molecular sieves made from common second degree building blocks,being layers of one or more than one unit cell thickness, wherein thelayer of more than one unit cell thickness is made from stacking,packing, or binding at least two monolayers of one unit cell thickness.The stacking of such second degree building blocks can be in a regularfashion, an irregular fashion, a random fashion, or any combinationthereof; and

(iv) molecular sieves made by any regular or random 2-dimensional or3-dimensional combination of unit cells having the MWW frameworktopology.

Molecular sieves of the MCM-22 family include those molecular sieveshaving an X-ray diffraction pattern including d-spacing maxima at12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom. The X-raydiffraction data used to characterize the material are obtained bystandard techniques using the K-alpha doublet of copper as incidentradiation and a diffractometer equipped with a scintillation counter andassociated computer as the collection system.

Materials of the MCM-22 family include MCM-22 (described in U.S. Pat.No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409), SSZ-25(described in U.S. Pat. No. 4,826,667), ERB-1 (described in EuropeanPatent No. 0293032), ITQ-1 (described in U.S. Pat. No. 6,077,498), ITQ-2(described in International Patent Publication No. WO97/17290), MCM-36(described in U.S. Pat. No. 5,250,277), MCM-49 (described in U.S. Pat.No. 5,236,575), MCM-56 (described in U.S. Pat. No. 5,362,697), andmixtures thereof. Related zeolite UZM-8 is also suitable for use as amolecular sieve component of the present catalyst.

In certain aspects, the molecular sieve employed in the aromatizationcatalyst may be an aluminosilicate or a substituted aluminosilicate inwhich part of all of the aluminum is replaced by a different trivalentmetal, such as gallium or indium.

In addition to the molecular sieve component, the aromatization catalystmay comprise at least one dehydrogenation component, e.g., at least onedehydrogenation metal. The dehydrogenation component is typicallypresent in an amount of at least 0.1 wt %, such as from 0.1 to 10 wt %,of the overall catalyst. The dehydrogenation component can comprise oneor more neutral metals selected from Groups 3 to 13 of the PeriodicTable of the Elements, such as Ga, In, Zn, Cu, Re, Mo, W, La, Fe, Ag,Pt, Pd, and/or one or more oxides, sulfides and/or carbides of thesemetals. The dehydrogenation component can be provided on the catalyst inany manner, for example by conventional methods such as impregnation orion exchange of the molecular sieve with a solution of a compound of therelevant metal, followed by conversion of the metal compound to thedesired form, namely neutral metal, oxide, sulfide and/or carbide. Partor all of the dehydrogenation metal may also be present in thecrystalline framework of the molecular sieve.

In one embodiment, the aromatization catalyst comprises ZSM-5 containingfrom 0.1 to 10 wt % Zn.

In some embodiments, the aromatization catalyst is selectivated, eitherbefore introduction into the aromatization reactor or in-situ in thereactor, by contacting the catalyst with a selectivating agent. In oneembodiment, the catalyst is silica-selectivated by contacting thecatalyst with at least one organosilicon in a liquid carrier andsubsequently calcining the silicon-containing catalyst in anoxygen-containing atmosphere, e.g., air, at a temperature of 350° C. to550° C. A suitable silica-selectivation procedure is described in U.S.Pat. No. 5,476,823, the entire contents of which are incorporated hereinby reference. In another embodiment, the catalyst is selectivated bycontacting the catalyst with steam. Steaming of the zeolite is effectedat a temperature of at least about 950° C., preferably about 950° C. toabout 1075° C., and most preferably about 1000° C. to about 1050° C.,for about 10 minutes to about 10 hours, preferably from 30 minutes to 5hours. The selectivation procedure, which may be repeated multipletimes, alters the diffusion characteristics of the catalyst and mayincrease the xylene yield during the aromatization process.

In addition to, or in place of, silica or steam selectivation, thecatalyst may be subjected to coke selectivation. This optional cokeselectivation typically involves contacting the catalyst with athermally decomposable organic compound at an elevated temperature inexcess of the decomposition temperature of said compound but below thetemperature at which the crystallinity of the molecular sieve isadversely affected. Further details regarding coke selectivationtechniques are provided in the U.S. Pat. No. 4,117,026, incorporated byreference herein. In some embodiments, a combination of silicaselectivation and coke selectivation may be employed.

Aromatization of the first product mixture may be conducted over a widerange of temperature and pressures. Thus in certain embodiments, thereaction is conducted at a temperature from 200° C. to 370° C. and apressure from 500 to 3,000 kPa (absolute), for example at a temperaturefrom 250° C. to 350° C. and a pressure from 700 to 2,000 kPa (absolute).Desirably, the F-T reaction and the aromatization reaction are conductedunder substantially the same conditions.

The F-T reaction and the aromatization reaction may be conducted inseparate catalyst beds arranged in series in separate or the samereaction vessel. Alternatively, the F-T reaction and the aromatizationreaction may be conducted in the same reaction bed with the first andsecond catalysts being stacked, mixed, or combined into a singlemulti-functional catalyst particle. In such a case, it will beappreciated the C₂₊ hydrocarbon product of the F-T reaction may beinstantaneously converted by the aromatization catalyst into a heavieraromatic-containing product.

Where the F-T and aromatization reactions are conducted in separatecatalyst beds, the effluent from the F-T reaction can be subjected toone or more separation steps to remove unreacted components, such asunreacted syngas, and reaction by-products, such as water, CO₂ and H₂,before the C₂₊ hydrocarbon product is forwarded to the aromatizationreaction. Optionally, the unreacted syngas is recycled to the F-Treaction.

The effluent from the aromatization reaction comprises a C₅₊ hydrocarbonproduct together with water, CO₂, H₂, and small quantities of C⁴⁻hydrocarbons. In certain embodiments, the reactor effluent productcomprises from 5 to 60 wt %, such as from 1 to 40 wt %, benzene and from1 to 20 wt % toluene. The aromatization effluent can be subjected to oneor more separation processes to remove unwanted by-products, such aswater and CO₂, and to recover H₂, which can be recycled to the F-Treaction, and C⁵⁻ hydrocarbons, which can be used as fuel. At least partof the benzene and toluene in the aromatization effluent is thenselectively methylated to produce para-xylene.

In certain aspects, methylation of the benzene and toluene in thearomatization effluent is conducted over a third catalyst, an alkylationcatalyst, comprising a molecular sieve having a Diffusion Parameter for2,2-dimethylbutane of about 0.1-15 sec⁻¹, such as 0.5-10 sec⁻¹, whenmeasured at a temperature of 120° C. and a 2,2-dimethylbutane pressureof 60 torr (8 kPa). As used herein, the Diffusion Parameter of aparticular porous crystalline material is defined as D/r²×10⁶, wherein Dis the diffusion coefficient (cm²/sec) and r is the crystal radius (cm).The required diffusion parameters can be derived from sorptionmeasurements provided the assumption is made that the plane sheet modeldescribes the diffusion process. Thus for a given sorbate loading Q, thevalue Q/Q_(∞), where Q_(∞) is the equilibrium sorbate loading, ismathematically related to (Dt/r²)^(1/2) where t is the time (sec)required to reach the sorbate loading Q. Graphical solutions for theplane sheet model are given by J. Crank in “The Mathematics ofDiffusion”, Oxford University Press, Ely House, London, 1967.

The molecular sieve employed in the present alkylation process isnormally a medium-pore size aluminosilicate zeolite. Medium porezeolites are generally defined as those having a pore size of about 5 toabout 7 Angstroms, such that the zeolite freely sorbs molecules such asn-hexane, 3-methylpentane, benzene and p-xylene. Another commondefinition for medium pore zeolites involves the Constraint Index testwhich is described in U.S. Pat. No. 4,016,218, which is incorporatedherein by reference. In this case, medium pore zeolites have aConstraint Index of about 1-12, as measured on the zeolite alone withoutthe introduction of oxide modifiers and prior to any steaming to adjustthe diffusivity of the catalyst. Particular examples of suitable mediumpore zeolites include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35,ZSM-48, and MCM-22, with ZSM-5 and ZSM-11 being particularly preferred.

The medium pore zeolites described above are particularly effective forthe present alkylation process since the size and shape of their poresfavor the production of p-xylene over the other xylene isomers. However,conventional forms of these zeolites have Diffusion Parameter values inexcess of the 0.1-15 sec⁻¹ range referred to above. However, therequired diffusivity for the catalyst can be achieved by severelysteaming the catalyst so as to effect a controlled reduction in themicropore volume of the catalyst to not less than 50%, and preferably50-90%, of that of the unsteamed catalyst. Reduction in micropore volumeis derived by measuring the n-hexane adsorption capacity of thecatalyst, before and after steaming, at 90° C. and 75 torr n-hexanepressure.

Steaming of the zeolite is effected at a temperature of at least about950° C., preferably about 950° C. to about 1075° C., and most preferablyabout 1000° C. to about 1050° C. for about 10 minutes to about 10 hours,preferably from 30 minutes to 5 hours.

To effect the desired controlled reduction in diffusivity and microporevolume, it may be desirable to combine the zeolite, prior to steaming,with at least one oxide modifier, such as at least one oxide selectedfrom elements of Groups 2 to 4 and 13 to 16 of the Periodic Table. Mostpreferably, said at least one oxide modifier is selected from oxides ofboron, magnesium, calcium, lanthanum and most preferably phosphorus. Insome cases, the zeolite may be combined with more than one oxidemodifier, for example a combination of phosphorus with calcium and/ormagnesium, since in this way it may be possible to reduce the steamingseverity needed to achieve a target diffusivity value. In someembodiments, the total amount of oxide modifier present in the catalyst,as measured on an elemental basis, may be between about 0.05 and about20 wt %, and preferably is between about 0.1 and about 10 wt %, based onthe weight of the final catalyst.

Where the modifier includes phosphorus, incorporation of modifier intothe catalyst is conveniently achieved by the methods described in U.S.Pat. Nos. 4,356,338; 5,110,776; 5,231,064; and 5,348,643, the entiredisclosures of which are incorporated herein by reference. Treatmentwith phosphorus-containing compounds can readily be accomplished bycontacting the zeolite, either alone or in combination with a binder ormatrix material, with a solution of an appropriate phosphorus compound,followed by drying and calcining to convert the phosphorus to its oxideform. Contact with the phosphorus-containing compound is generallyconducted at a temperature of about 25° C. and about 125° C. for a timebetween about 15 minutes and about 20 hours. The concentration of thephosphorus in the contact mixture may be between about 0.01 and about 30wt %. Suitable phosphorus compounds include, but are not limited to,phosphonic, phosphinous, phosphorus and phosphoric acids, salts andesters of such acids, and phosphorous halides.

After contacting with the phosphorus-containing compound, the porouscrystalline material may be dried and calcined to convert the phosphorusto an oxide form. Calcination can be carried out in an inert atmosphereor in the presence of oxygen, for example, in air at a temperature ofabout 150° C. to 750° C., preferably about 300° C. to 500° C., for atleast 1 hour, preferably 3-5 hours. Similar techniques known in the artcan be used to incorporate other modifying oxides into the catalystemployed in the alkylation process.

In addition to the zeolite and modifying oxide, the catalyst employed inthe alkylation process may include one or more binder or matrixmaterials resistant to the temperatures and other conditions employed inthe process. Such materials include active and inactive materials suchas clays, silica, and/or metal oxides, such as alumina. The latter maybe either naturally occurring or in the form of gelatinous precipitatesor gels including mixtures of silica and metal oxides. Use of a materialwhich is active, tends to change the conversion and/or selectivity ofthe catalyst and hence is generally not preferred. Inactive materialssuitably serve as diluents to control the amount of conversion in agiven process so that products can be obtained economically and orderlywithout employing other means for controlling the rate of reaction.These materials may be incorporated into naturally occurring clays,e.g., bentonite and kaolin, to improve the crush strength of thecatalyst under commercial operating conditions. Said materials, i.e.,clays, oxides, etc., function as binders for the catalyst. It isdesirable to provide a catalyst having good crush strength because incommercial use it is desirable to prevent the catalyst from breakingdown into powder-like materials. These clay and/or oxide binders havebeen employed normally only for the purpose of improving the crushstrength of the catalyst.

Naturally occurring clays which can be composited with the porouscrystalline material include the montmorillonite and kaolin family,which families include the subbentonites and the kaolins commonly knownas Dixie, McNamee, Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite, oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment, or chemicalmodification.

In addition to the foregoing materials, the porous crystalline materialcan be composited with a porous matrix material such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia,and silica-magnesia-zirconia.

The relative proportions of porous crystalline material and inorganicoxide matrix vary widely, with the content of the former ranging fromabout 1 to about 90% by weight and more usually, particularly when thecomposite is prepared in the form of beads, in the range of about 2 toabout 80 wt % of the composite. Preferably, the matrix materialcomprises silica or a kaolin clay.

The alkylation catalyst used in the present process may optionally beprecoked. The precoking step is may be carried out by initially loadinguncoked catalyst into the methylation reactor. Then, as the reactionproceeds, coke is deposited on the catalyst surface and thereafter maybe controlled within a desired range, typically from about 1 to about 20wt % and preferably from about 1 to about 5 wt %, by periodicregeneration by exposure to an oxygen-containing atmosphere at anelevated temperature.

In certain aspects, methylation of the benzene and toluene in thearomatization effluent is effected with a methylating agent comprisingmethanol and/or a mixture of carbon monoxide and hydrogen. In the lattercase, the molar ratio of hydrogen to carbon monoxide in the methylatingagent may comprise from 1 to 4, such as from 1.5 to 3.0. Suitableconditions for the methylation reaction a temperature from 350° C. to700° C., preferably from 500° C. to 600° C., a pressure of from 100 and2000 kPa absolute, a weight hourly space velocity of from 0.5 to 1000hr⁻¹, and a molar ratio of toluene to methanol (in the reactor charge)of at least about 0.2, e.g., from about 2 to about 20. The process maysuitably be carried out in fixed, moving, or fluid catalyst beds. If itis desired to continuously control the extent of coke loading, moving orfluid bed configurations are preferred. With moving or fluid bedconfigurations, the extent of coke loading can be controlled by varyingthe severity and/or the frequency of continuous oxidative regenerationin the catalyst regenerator.

Using the present process, toluene can be alkylated with methanol so asto produce para-xylene at a selectivity of at least about 80 wt % (basedon total C₈ aromatic product) at a per-pass aromatic conversion of atleast about 15 wt % and a trimethylbenzene production level less than 1wt %. Unreacted benzene and toluene and methylating agent and a portionof the water by-product may be recycled to the methylation reactor andheavy byproducts routed to fuels dispositions. The C₈ fraction is routedto a para-xylene recovery unit, which typically operates by fractionalcrystallization or by selective adsorption (e.g. Parex or Eluxyl) torecover a para-xylene product stream from the alkylation effluent andleave a para-xylene-depleted stream containing mainly C₇ and C₈hydrocarbons. The para-xylene-depleted stream may be isomerized andrecycled to the para-xylene recovery unit.

In certain embodiments, the F-T synthesis, aromatization, andpara-selective alkylation of benzene or toluene are conducted in asingle reaction zone, the reaction zone utilizing a first catalyst forthe F-T synthesis and a second catalyst for aromatizing the F-T productsto selectively alkylate the benzene and/or toluene to produce p-xylene.For example, the reactions may be carried out substantiallysimultaneously in a single vessel containing a single catalyst bed. Insuch embodiments, the catalyst bed can contain a mixture of thecatalysts or at least one multi-functional catalyst. A multi-functionalcatalyst may comprise a first catalytic functionality to accomplish F-Tsynthesis, a second catalytic functionality to accomplish aromatization,and a third catalytic functionality to accomplish selectivebenzene/toluene alkylation. In one embodiment, the second and thirdcatalytic functionalities are combined into a single functionality foraromatization and selective aromatics alkylation. For example, themulti-functional catalyst can be a composite catalyst which comprises,e.g., (i) one or more metals selected from Fe, Co, or Cu, the metalbeing in combination with one or more supports comprising ZnO, MnO,Al₂O₃, SiO₂, or carbonaceous supports such as one or more of activatedcarbon, carbon black, carbonaceous nanotubes, or carbonaceousnanofibers, and (ii) silica-selectivated ZSM-5 containing one or moremetals selected from Groups 10-14 of the Periodic Table, such assilica-selectivated ZSM-5 containing one or more of Zn, Ga, Cu, Ag, Mg,Ho, Sr, or Pt.

The single reaction zone operates at conditions including a temperaturein the range of about 200° C. to 360° C., a pressure in the range ofabout 300 to 5,000 kPa (absolute), and a syngas H₂:CO (mol) ratio in therange of about 0.5 to 4.

The invention will now be more particularly described with reference tothe following non-limiting Example and the accompanying drawing.

EXAMPLE

Equilibrium concentrations for the components of the effluent from theconversion of syngas with varying H₂/CO molar compositions show that theconversion of syngas to p-xylene is possible and favored among the otheraromatics allowed in the simulation based on equilibrium across theoperating conditions displayed, a temperature of 270° C. and a pressureof 1100 kPa (absolute) as shown in the FIGURE. The xylene isomers wererestricted to p-xylene in the calculation to show the maximum potentialyield from a shape selective catalyst.

The description and examples above support one or more of the followingmore specific Embodiments.

Embodiment 1. A process for producing xylenes, the process comprising:

(a) providing a first feed comprising hydrogen and carbon monoxide, inwhich the molar ratio of hydrogen to carbon monoxide is from about 0.5to 6;

(b) contacting the first feed with (i) a first catalyst comprising atleast one metal or compound containing a metal selected from the groupconsisting of Fe, Co, Cr, Cu, Zn, Mn, and Ru, and (ii) a secondcatalyst, which may be the same as or different than the first catalyst,comprising at least one medium pore size molecular sieve underconditions including a temperature from 200° C. to 370° C. and apressure from 500 to 3000 kPa (absolute) effective to produce a reactioneffluent containing benzene and/or toluene; and

(c) reacting at least part of the benzene and/or toluene in the reactioneffluent with a second feed comprising (i) methanol and/or (ii) hydrogenand carbon monoxide under conditions effective to produce p-xylene,wherein the reacting is conducted in the presence of a third catalystcomprising at least one molecular sieve having a Diffusion Parameter for2,2-dimethylbutane of from 0.1 to 15 sec⁻¹ when measured at atemperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8kPa).

Embodiment 2. The process of Embodiment 1, wherein the first catalystfurther comprises a support selected from the group consisting of zincoxide, manganese oxide, alumina, silica, carbon, and mixtures thereof.

Embodiment 3. The process of Embodiment 1 or Embodiment 2, wherein firstcatalyst further comprises at least one stabilizer selected from anelement or a compound thereof, wherein the element is selected fromGroups 1 to 4 of the Periodic Table of the Elements.

Embodiment 4. The process of Embodiment 3, wherein the element fromGroups 1 to 4 of the Periodic Table is selected from the groupconsisting of Cs, K, and Ca.

Embodiment 5. The process of any one of Embodiments 1-4, wherein thesecond catalyst comprises at least one molecular sieve having aConstraint Index of 1-12.

Embodiment 6. The process of any one of Embodiments 1-5, wherein the atleast one molecular sieve of the second catalyst comprises ZSM-5.

Embodiment 7. The process of any one of Embodiments 1-6, wherein thesecond catalyst comprises at least one metal or a compound thereof,wherein the metal is selected from the group consisting of Ga, In, Zn,Cu, Re, Mo, W, La, Fe, Ag, Pt, and Pd.

Embodiment 8. The process of any one of Embodiments 1-7, wherein thesecond catalyst is selectivated by at least one of silica, steam orcoke.

Embodiment 9. The process of any one of Embodiments 1-8, wherein thefirst and second catalysts are located in different reactions beds.

Embodiment 10. The process of any one of Embodiments 1-8, wherein thefirst and second catalysts are different but are located in the samereaction bed.

Embodiment 11. The process of any one of Embodiments 1-8, wherein thefirst and second catalysts are combined into a single multi-functionalcatalyst.

Embodiment 12. The process of any one of Embodiments 1-11, wherein theat least one molecular sieve of the third catalyst comprises ZSM-5.

Embodiment 13. The process of any one of Embodiments 1-12, wherein thereacting (c) is conducted under conditions including a temperature from350 to 700° C., a pressure of from 100 and 7000 kPa absolute, and aweight hourly space velocity of from 0.5 to 300 hr⁻¹.

Embodiment 14. A catalyst system for the production of para-xylenecomprising:

(a) a first catalyst comprising at least one metal or compound thereof,wherein the metal is selected from the group consisting of Fe, Co, Cr,Cu, Zn, Mn, and Ru, and

(b) a second catalyst, which may be the same as or different than thefirst catalyst, comprising at least one medium pore size molecular sieveand at least one metal or compound thereof, wherein the metal isselected from Groups 10-14 of the Periodic Table,

wherein the first and second catalysts are located within the samereactor bed.

Embodiment 15. The catalyst system of Embodiment 14 wherein the firstand second catalysts are different and are physically mixed in the samereactor bed.

Embodiment 16. The catalyst system of Embodiment 14 wherein the firstand second catalysts are combined into a single multi-functionalcatalyst.

Embodiment 17. The catalyst system of any one of Embodiments 14-16,wherein the first catalyst comprises a metal selected from the groupconsisting of Fe, Co, and Cu, and at least one support selected from thegroup consisting of zinc oxide, manganese oxide, alumina, silica,carbon, and mixtures thereof.

Embodiment 18. The catalyst system of any one of Embodiments 14-17,wherein the second catalyst comprises at least one metal or compoundthereof, wherein the metal is selected from the group consisting of Ga,In, Zn, Cu, Re, Mo, W, La, Fe, Ag, Pt, and Pd.

Embodiment 19. The catalyst system of any one of Embodiments 14-18,wherein the metal of the second catalyst is present in an amount ofabout 0.1 to 10 wt %.

Embodiment 20. The catalyst system of any one of Embodiments 14-19,wherein the second catalyst comprises silica-selectivated ZSM-5.

All patents, test procedures, and other documents cited herein,including priority documents, are fully incorporated by reference to theextent such disclosure is not inconsistent and for all jurisdictions inwhich such incorporation is permitted.

While the illustrative forms disclosed herein have been described withparticularity, it will be understood that various other modificationswill be apparent to and can be readily made by those skilled in the artwithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the scope of the claims appendedhereto be limited to the examples and descriptions set forth herein butrather that the claims be construed as encompassing all the features ofpatentable novelty which reside herein, including all features whichwould be treated as equivalents thereof by those skilled in the art towhich this disclosure pertains.

When numerical lower limits and numerical upper limits are listedherein, ranges from any lower limit to any upper limit are contemplated,and are expressly within the scope of the invention. The term“comprising” is synonymous with the term “including”. Likewise whenevera composition, an element or a group of components is preceded with thetransitional phrase “comprising”, it is understood that we alsocontemplate the same composition or group of components withtransitional phrases “consisting essentially of,” “consisting of”,“selected from the group of consisting of,” or “is” preceding therecitation of the composition, component, or components, and vice versa.

The invention claimed is:
 1. A process for producing xylenes, theprocess comprising: (a) providing a first feed comprising hydrogen andcarbon monoxide, in which the molar ratio of hydrogen to carbon monoxideis from about 0.5 to 6; (b) contacting the first feed with (i) a firstcatalyst comprising 1 to 50 wt % of Fe, and (ii) a second catalystcomprising at least one medium pore size molecular sieve, whereincontacting the first feed with the first catalyst and the secondcatalyst is carried out under conditions including a temperature from200° C. to 370° C. and a pressure from 500 to 3000 kPa (absolute)effective to produce a reaction effluent containing benzene and/ortoluene; and (c) reacting at least part of the benzene and/or toluene inthe reaction effluent with a second feed comprising (i) methanol and/or(ii) hydrogen and carbon monoxide under conditions effective to producep-xylene, wherein the reacting is conducted in the presence of a thirdcatalyst comprising at least one molecular sieve having a DiffusionParameter for 2,2-dimethylbutane of from 0.1 to 15 sec⁻¹ when measuredat a temperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr(8kPa), wherein the second catalyst is selectivated by contacting thesecond catalyst with steam at a temperature of at least 950° C. forabout 10 minutes to 10 hours.
 2. The process of claim 1, wherein thefirst catalyst further comprises a support selected from the groupconsisting of zinc oxide, manganese oxide, alumina, silica, carbon, andmixtures thereof.
 3. The process of claim 1, wherein first catalystfurther comprises at least one stabilizer selected from an element or acompound thereof, wherein the element is selected from Groups 1 to 4 ofthe Periodic Table of the Elements.
 4. The process of claim 3, whereinthe element from Groups 1 to 4 of the Periodic Table is selected fromthe group consisting of Cs, K, and Ca.
 5. The process of claim 1,wherein the second catalyst comprises at least one molecular sievehaving a Constraint Index of 1 -12.
 6. The process of claim 1, whereinthe at least one medium pore size molecular sieve of the second catalystcomprises ZSM-5.
 7. The process of claim 1, wherein the second catalystcomprises at least one metal or a compound thereof, wherein the metal isselected from the group consisting of Ga, In, Zn, Cu, Re, Mo, W, La, Fe,Ag, Pt, and Pd.
 8. The process of claim 1, wherein the first and secondcatalysts are located in different reactions beds.
 9. The process ofclaim 1, wherein the first and second catalysts are different but arelocated in the same reaction bed.
 10. The process of claim 1, whereinthe first and second catalysts are combined into a singlemulti-functional catalyst.
 11. The process of claim 1, wherein the atleast one molecular sieve of the third catalyst comprises ZSM-5.
 12. Theprocess of claim 1, wherein the reacting (c) is conducted underconditions including a temperature from 350 to 700° C., a pressure offrom 100 and 7000 kPa absolute, and a weight hourly space velocity offrom 0.5 to 300 hr⁻¹.
 13. The process of claim 1, wherein the firstcatalyst further comprises 0.1 to 20 wt % of Cu.